Power transmission belts comprising an elastomeric body reinforced with one or more helical winds of a cord, such as fiber glass and the like treated to bond to the elastomer to thus form a tension member are well known in the art. Some belts also include members to provide lateral stiffness to the belt while permitting longitudinal flexibility thereto when used to transmit power especially in variable pulley drives in which the belt performs its power transmission function by engaging the pulley flanges with its edges. In the absence of the stiffeners, belts especially when used in variable pulley drives sag in the middle, become arched and distorted. This is considered to be undesirable and is to be avoided. Examples of belts with lateral stiffening means are described in U.S. patents to Unger and Redmond, U.S. Pat. Nos. 2,189,049 and 3,772,929, respectively.